Coating Fine Iron Particles with an Oxidation-Resistant Alumina Nanolayer using Atomic Layer Deposition in a Fluidized Bed Reactor

摘要

Very fine (～5 μm) iron (Fe) particles are coated with an ultrathin, conformal, pinhole-free, crystalline γ-alumina nanolayer on the order of 1-10 nm using Atomic Layer Deposition (ALD) in a fluidized bed reactor. While fluidizing, the individual primary particles form aggregates that are approximately 96 μm based upon laser imaging. The primary particles are found to have a very thin (～3-5 nm) layer of hematite (α-Fe{sub}2O{sub}3) on their surface. After the coating process, the particle size distribution (PSD) and surface area are not changed from the starting values prior to coating, indicating that the coatings do not bind the aggregates together. All individual primary particles are coated, regardless of aggregation during fluidization, due to the nature of the ALD process. Uncoated particles begin to oxidize in air at 473 K. Once the coating is thicker than 2.5 nm, the particles will not oxidize in air at temperatures up to 723 K. The magnetic moment of the particles is unaffected by the protective coating.